Re: restoring old jemalloc patches

[coypu%sdf.org@localhost]

On Thu, Jul 11, 2019 at 10:30:52PM +0000, coypu%sdf.org@localhost wrote:
> hi folks, while skimming jemalloc, noticed a comment about our old code
> being better.

         * Ideally, there would be a way to specify alignment to mmap() (like
         * NetBSD has), but in the absence of such a feature, we have to work
         * hard to efficiently create aligned mappings.  The reliable, but
         * slow method is to create a mapping that is over-sized, then trim the
         * excess.  However, that always results in one or two calls to
         * os_pages_unmap(), and it can leave holes in the process's virtual
         * memory map if memory grows downward.
         *
         * Optimistically try mapping precisely the right amount before falling
         * back to the slow method, with the expectation that the optimistic
         * approach works most of the time.

So if that doesn't work, it'll loop in pages_map_slow, hoping to get aligned
stuff.